JP2008211591A - Photoelectric converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric converter which corrects an optical signal at high precision and is made easy to respond to speed acceleration. <P>SOLUTION: The photoelectric converter is provided with: an optical signal common output line 10 which is commonly connected to all photoelectric conversion units 30, outputs each amplification optical signal from each photoelectric conversion unit 30 in time series and has a first parasitic capacity 31; an initial voltage common output line 11 which is commonly connected to all the photoelectric conversion unit 30, outputs each amplification initial voltage from each photoelectric conversion unit 30 in time series and has a second parasitic capacity 32 and a capacity group 20 which is connected to the optical signal common output line 10 or the initial voltage common output lien 11 and has a capacity value approximately equal to a differential capacity value between the first parasitic capacity 31 and the second parasitic capacity 32. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device that outputs an output voltage based on incident light.

  Currently, photoelectric conversion devices are used as image reading devices such as facsimiles, image scanners, digital copying machines, and X-ray imaging devices. A photoelectric conversion device is manufactured using a single crystal silicon chip, and a contact image sensor (CIS) is well known.

  Here, a conventional photoelectric conversion device will be described.

  The photoelectric conversion device includes a plurality of photodiodes, a noise signal holding unit that reads and holds a noise signal from the photodiodes, and an optical signal holding unit that reads and holds an optical signal from the photodiodes. The photoelectric conversion device includes a noise signal common output line that is connected to each photodiode and outputs a noise signal, and an optical signal common output line that is connected to each photodiode and outputs an optical signal. Further, the photoelectric conversion device is configured to divide the noise signal held by the noise signal holding unit and the optical signal held by the optical signal holding unit into a capacity divided by a capacity of the noise signal common output line and a capacity of the optical signal common output line. A reading means for reading is provided. In addition, the photoelectric conversion device is provided between the noise signal common output line and the optical signal common output line, and is turned on to eliminate voltage imbalance between the noise signal common output line and the optical signal common output line. A switch for correcting the optical signal with high accuracy is provided (for example, see Patent Document 1).

In this way, even if integration with single crystal silicon chips progresses, the density of elements and metal wiring increases, and the mask layout design between the noise signal common output line and the optical signal common output line becomes unbalanced, the noise signal It is possible to correct the optical signal with high accuracy by eliminating voltage imbalance between the common output line and the optical signal common output line.
JP-A-10-191173

  However, in order to correct the optical signal with high accuracy, the switch provided between the noise signal common output line and the optical signal common output line is turned on and then turned off. Since the data is read out to the common output line and the optical signal common output line, the time for reading out the noise signal and the optical signal is shortened by the time for which the switch operates. Therefore, it is difficult to increase the speed of the photoelectric conversion device.

  The present invention has been made in view of the above points, and provides a photoelectric conversion device that can correct an optical signal with high accuracy and easily cope with high speed.

  In order to solve the above problems, the present invention provides a photoelectric conversion device that outputs an output voltage based on incident light, an optical signal output unit that outputs an optical signal based on the incident light, and an output of the optical signal output unit A reset means for resetting the voltage of the output terminal of the optical signal output means to a predetermined initial voltage, and an output terminal of the optical signal output means for amplifying the optical signal to obtain an amplified optical signal. Amplifying means for outputting and amplifying the initial voltage to output an amplified initial voltage; an optical signal holding means connected to the output terminal of the amplifying means for holding the amplified optical signal; and an output terminal of the amplifying means And a plurality of photoelectric conversion units having an initial voltage holding means for holding the amplified initial voltage, and connected in common to all the photoelectric conversion units, Amplified optical signals are output in time series, and are connected in common to the optical signal common output line having the first parasitic capacitance and all the photoelectric conversion units, and the amplified initial voltages from the photoelectric conversion units are An initial voltage common output line that outputs in series and has a second parasitic capacitance, and is connected to the optical signal common output line or the initial voltage common output line, and the difference between the first parasitic capacitance and the second parasitic capacitance There is provided a photoelectric conversion device comprising: an adjustment capacitor having a capacitance value substantially equal to a capacitance value; and a subtraction amplifier that subtracts the amplified initial voltage from the amplified optical signal.

  In the present invention, the adjustment capacitor having a capacitance value substantially equal to the differential capacitance value between the first parasitic capacitance by the optical signal common output line and the second parasitic capacitance by the initial voltage common output line is the optical signal common output line or the initial voltage common output. Since they are connected to the line, the parasitic capacitance due to the optical signal common output line is equal to the parasitic capacitance due to the initial voltage common output line. Therefore, the influence of the parasitic capacitance on the optical signal is eliminated, and the optical signal is corrected with high accuracy.

  In addition, the adjustment capacitor is connected to the optical signal common output line or the initial voltage common output line, and this adjustment capacitor is not controlled by a signal, and no time is required for controlling the adjustment capacitor, so the optical signal and the initial voltage are read out. Time will not be shortened. Therefore, the photoelectric conversion device can easily cope with speeding up.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, a configuration of a photoelectric conversion unit mounted on a photoelectric conversion device that outputs an output voltage based on incident light will be described. FIG. 1 is a circuit diagram showing a photoelectric conversion unit.

  The photoelectric conversion unit 30 includes a photodiode 1, a reset switch 2, a buffer amplifier 3, a switch 14, a switch 15, a capacitor 12, a capacitor 13, a switch 16, and a switch 17.

  The reset switch 2 and the buffer amplifier 3 are connected to the output terminal of the photodiode 1. The capacitor 12 is connected to the output terminal of the buffer amplifier 3 via the switch 14, and the capacitor 13 is connected to the output terminal of the buffer amplifier 3 via the switch 15. The capacitor 12 is connected to the optical signal common output line 10 via a switch 16, and the capacitor 13 is connected to the initial voltage common output line 11 via a switch 17.

  The photodiode 1 generates a photocharge based on incident light and outputs an optical signal based on the photocharge. The reset switch 2 resets the voltage at the output terminal of the photodiode 1 to a predetermined initial voltage. The buffer amplifier 3 amplifies the optical signal and outputs an amplified optical signal, amplifies the initial voltage, and outputs an amplified initial voltage. The capacitor 12 holds the amplified optical signal, and the capacitor 13 holds the amplified initial voltage.

  Next, the structure of the front | former part of a photoelectric conversion apparatus is demonstrated. FIG. 2 is a circuit diagram illustrating a front part of the photoelectric conversion device.

  The front stage portion of the photoelectric conversion device includes a plurality of photoelectric conversion units 30, an optical signal common output line 10, an initial voltage common output line 11, a switch 18, a switch 19, a capacitor group 20, a metal wiring 20z, a first parasitic capacitance 31, and a first Two parasitic capacitances 32 are provided.

  The optical signal common output line 10 is commonly connected to all the photoelectric conversion units 30 and has a first parasitic capacitance 31. The initial voltage common output line 11 is commonly connected to all the photoelectric conversion units 30 and has a second parasitic capacitance. Further, the voltage Vclamp1 is applied to the optical signal common output line 10 via the switch 18. A voltage Vclamp1 is applied to the initial voltage common output line 11 via the switch 19. The capacitor group 20 is connected to the optical signal common output line 10 or the initial voltage common output line 11.

  The optical signal common output line 10 outputs each amplified optical signal from each photoelectric conversion unit 30 in time series, and the initial voltage common output line 11 outputs each amplified initial voltage from each photoelectric conversion unit 30 in time series. Output to. The capacitance group 20 has a capacitance value approximately equal to the differential capacitance value between the first parasitic capacitance 31 and the second parasitic capacitance 32.

  Next, the structure of the latter part of the photoelectric conversion device will be described. FIG. 3 is a circuit diagram illustrating a rear part of the photoelectric conversion device.

  The rear stage portion of the photoelectric conversion device includes a buffer amplifier 22, a buffer amplifier 23, a subtraction amplifier 24, a clamp circuit 25, a buffer amplifier 26, a sample hold circuit 27, a buffer amplifier 28, and a transmission gate 29.

  The optical signal common output line 10 is connected to the subtraction amplifier 24 via the buffer amplifier 22, and the initial voltage common output line 11 is connected to the subtraction amplifier 24 via the buffer amplifier 23. The output terminal of the subtraction amplifier 24 is connected to the clamp circuit 25, and the output terminal of the clamp circuit 25 is connected to the buffer amplifier 26. The output terminal of the buffer amplifier 26 is connected to the sample hold circuit 27, the output terminal of the sample hold circuit 27 is connected to the buffer amplifier 28, and the output terminal of the buffer amplifier 28 is connected to the transmission gate 29.

  Next, the operation of the photoelectric conversion unit 30 will be described.

  The reset switch 2 is turned on by the signal φR. Then, the voltage Vdi at the output terminal of the photodiode 1 becomes the reset voltage Vreset. Thereafter, the reset switch 2 is turned off by the signal φR. Then, the voltage Vdi becomes a voltage obtained by adding the noise voltage Voff from the photodiode 1 to the reset voltage Vreset (hereinafter referred to as an initial voltage). Immediately after the reset switch 2 is turned off, the switch 15 is turned on by the signal φRIN, the initial voltage becomes the amplified initial voltage VBITR via the buffer amplifier 3 controlled by the signal φSEL, and this amplified initial voltage VBITR is read out to the capacitor 13. . The amplified initial voltage VBITR is read until the switch 15 is turned off after the reset switch 2 is turned off.

  Thereafter, the photodiode 1 generates and holds a photocharge based on the incident light, and the voltage Vdi varies based on the amount of the photocharge. Then, the voltage Vdi becomes a voltage (hereinafter referred to as an optical signal) obtained by adding the voltage based on the noise voltage Voff by the photodiode 1 and the amount of photoelectric charge held by the photodiode 1 to the reset voltage Vreset. The switch 14 is turned on by the signal φSIN, and the optical signal becomes the amplified optical signal VBITS through the buffer amplifier 3, and this amplified optical signal VBITS is read out to the capacitor 12. The amplified optical signal VBITS is read until the switch 14 is turned off after the reset switch 2 is turned off.

  When the switch 16 and the switch 17 are simultaneously turned on based on the signal φSCH and a predetermined condition is satisfied, the amplified optical signal VBITS and the initial voltage VBITR are read out to the optical signal common output line 10 and the initial voltage common output line 11, respectively. . The subsequent circuit subtracts the initial voltage VBITR from the amplified optical signal VBITS, whereby an output voltage based on the photocharge based on the incident light is extracted.

  The operation of reading the amplified initial voltage VBITR to the capacitor 13 and the operation of reading the amplified optical signal VBITS to the capacitor 12 are repeated.

  Next, the operation of the front part of the photoelectric conversion device will be described.

  Here, each photoelectric conversion unit 30 outputs the amplified optical signal VBITS and the amplified initial voltage VBITR in time series.

  When the signal φSCH becomes high and the signal φclamp1 becomes low (hereinafter referred to as the first half period), the switch 16 and the switch 17 are turned on, and the switch 18 and the switch 19 are turned off. Therefore, the amplified optical signal VBITS from the predetermined photoelectric conversion unit 30 held in the capacitor 12 is read out to the optical signal common output line 10 by the voltage division ratio between the capacitor 12 and the first parasitic capacitor 31, and at the same time, the capacitor The amplified initial voltage VBITR from the predetermined photoelectric conversion unit 30 held at 13 is read out to the initial voltage common output line 11 by the voltage dividing ratio between the capacitor 13 and the first parasitic capacitor 32.

  When the signal φSCH becomes high and the signal φclamp1 becomes high (hereinafter referred to as the second half period), the switch 16 and the switch 17 are turned on, and the switch 18 and the switch 19 are also turned on. Therefore, the voltages of the optical signal common output line 10 and the initial voltage common output line 11 are initialized to the voltage Vclamp1.

  The optical signal common output line 10 has a first parasitic capacitance 31 and is affected by the first parasitic capacitance 31. The initial voltage common output line 11 has a second parasitic capacitance 32 and is affected by the second parasitic capacitance 32. Further, the optical signal common output line 10 or the initial voltage common output line 11 includes a capacitance group 20 having a capacitance value approximately equal to the differential capacitance value between the first parasitic capacitance 31 and the second parasitic capacitance 32, and the capacitance group 20 Is influenced by. Therefore, the influence of the capacitance on the optical signal common output line 10 is equal to the influence of the capacitance on the initial voltage common output line 11.

  Here, for example, the amplification factors of the buffer amplifier 3, the buffer amplifier 22, and the buffer amplifier 23 are about 1 time, the amplification rate of the subtraction amplifier 24 is about 4 times, and the amplification rates of the buffer amplifier 26 and the buffer amplifier 28 are About twice. Before the amplified optical signal VBITS and the amplified initial voltage VBITR are greatly amplified, the influence of the capacitance on the optical signal common output line 10 becomes equal to the influence of the capacitance on the initial voltage common output line 11.

  Next, the operation of the latter part of the photoelectric conversion device will be described.

  Here, each photoelectric conversion unit 30 outputs the amplified optical signal VBITS and the amplified initial voltage VBITR in time series.

  In the first half period, the amplified optical signal VBITS from the predetermined photoelectric conversion unit 30 is input to the subtraction amplifier 24 via the buffer amplifier 22, and the amplified initial voltage VBITR from the predetermined photoelectric conversion unit 30 is also subtracted via the buffer amplifier 23. Input to the amplifier 24. The subtraction amplifier 24 subtracts the amplified initial voltage VBITR from the amplified optical signal VBITS, thereby removing the noise voltage Voff of the amplified optical signal VBITS. The output signal of the first half period of the subtraction amplifier 24 is a signal obtained by subtracting the amplified initial voltage VBITR from the amplified optical signal VBITS, multiplying it by a gain, and adding the reference voltage VREF.

  In the second half period, the voltage Vclamp1 is input to the subtraction amplifier 24 via the buffer amplifier 22 and the buffer amplifier 23. Therefore, since the two input terminals of the subtraction amplifier 24 have no voltage difference, the output signal of the second half period of the subtraction amplifier 24 becomes the reference voltage VREF.

  Here, in the first half period and the second half period, the offsets of the buffer amplifier 22, the buffer amplifier 23, and the subtraction amplifier 24 are on the output signal of the subtraction amplifier 24. The output signal of the subtracting amplifier 24 is input to the clamp circuit 25.

  In the latter half period, a terminal to which the reference voltage VREF is applied is connected to the output terminal of the clamp circuit 25 through the switch circuit, although not shown, based on the clamp pulse φCLAMP to the clamp circuit 25. Therefore, the output signal in the second half period of the clamp circuit 25 is clamped to the reference voltage VREF.

  In addition, although not shown, the terminal to which the reference voltage VREF is applied is not connected to the output terminal of the clamp circuit 25 based on the clamp pulse φCLAMP in the first half period. Therefore, a capacitor is provided between the input terminal and the output terminal of the clamp circuit 25, and the output signal of the first half period of the clamp circuit 25 is changed from the output signal of the first half period of the subtraction amplifier 24 at the input terminal to the output terminal. A signal obtained by subtracting the output signal of the latter half period one period before the clamp circuit 25 clamped to the reference voltage VREF is added to the reference voltage VREF. Therefore, the output signal of the first half period of the clamp circuit 25 is a signal obtained by subtracting the amplified initial voltage VBITR from the amplified optical signal VBITS and multiplying the gain by adding the reference voltage VREF. Note that the offsets of the buffer amplifier 22, the buffer amplifier 23, and the differential amplifier 24 do not ride on the output signal of the first half period of the clamp circuit 25.

  The output signal of the clamp circuit 25 is input to the buffer amplifier 26. An output signal of the buffer amplifier 26 is input to the sample hold circuit 27.

  In the first half period, the sample hold circuit 27 samples the output signal of the buffer amplifier 26 based on the output signal of the first half period of the clamp circuit 25 based on the sample hold pulse φSH to the sample hold circuit 27.

  In the second half period, the sample hold circuit 27 holds the sampled signal based on the sample hold pulse φSH, and the output signal of the sample hold circuit 27 is maintained for a long period.

  The output signal of the sample hold circuit 27 is input to the buffer amplifier 28. The output signal of the buffer amplifier 28 is input to the transmission gate 29. The transmission gate 29 outputs an output voltage VOUT based on the photocharge based on the incident light.

  In this way, the capacitance group 20 having a capacitance value almost equal to the differential capacitance value between the first parasitic capacitance 31 by the optical signal common output line 10 and the second parasitic capacitance 32 by the initial voltage common output line 11 is output to the optical signal common output. Since it is connected to the line 10 or the initial voltage common output line 11, the parasitic capacitance due to the optical signal common output line 10 is equal to the parasitic capacitance due to the initial voltage common output line 11. Therefore, the influence of the parasitic capacitance on the optical signal is eliminated, and the optical signal is corrected with high accuracy.

  In addition, the capacitor group 20 is connected to the optical signal common output line 10 or the initial voltage common output line 11, and the capacitor group 20 is not controlled by a signal, and no time is required for controlling the capacitor group 20. And the time for reading the initial voltage is not shortened. Therefore, the photoelectric conversion device can easily cope with speeding up.

  Even if the number of photodiodes 1 increases or decreases or the number of photoelectric conversion units 30 increases or decreases, the parasitic capacitance due to the optical signal common output line 10 and the parasitic capacitance due to the initial voltage common output line 11 based on the state at that time. And become equal. Therefore, regardless of the number of photodiodes 1 and the number of photoelectric conversion units 30, the influence of the parasitic capacitance on the optical signal is eliminated, and the optical signal is corrected with high accuracy.

  Next, the capacity group 20 will be described. FIG. 4 is a diagram illustrating the first capacity group.

  As shown in FIG. 4, the capacitor group 20 has a plurality of capacitors 20a and a plurality of metal wirings 20b. A plurality of capacitors 20a having the same capacitance value may be prepared, or a plurality of capacitors 20a having different capacitance values may be prepared. In each capacitor, the capacitor 20a is connected to the optical signal common output line 10 or the initial voltage common output line 11 through the corresponding metal wiring 20b.

  Thus, the mask used for manufacturing the semiconductor device is changed and the metal wiring 20b is changed, so that the capacitance 20c connected to the optical signal common output line 10 or the initial voltage common output line 11 is changed. The number is changed, and the capacitance value of the capacitance group 20 is trimmed. Therefore, a capacitance value that is almost equal to the differential capacitance value between the first parasitic capacitance 31 and the second parasitic capacitance 32 is easily realized.

  Next, a capacity group 20 different from the above will be described. FIG. 5 is a diagram illustrating the second capacity group.

  As shown in FIG. 5, the capacitance group 20 includes a plurality of capacitors 20c and a plurality of switches 20d. A plurality of capacitors 20c having the same capacitance value may be prepared, or a plurality of capacitors 20c having different capacitance values may be prepared. In each capacitor, the capacitor 20c is connected to the optical signal common output line 10 or the initial voltage common output line 11 via the corresponding switch 20d.

  In this way, by controlling on / off of the switch 20d, the number of capacitors 20a connected to the optical signal common output line 10 or the initial voltage common output line 11 is changed, and the capacitance value of the capacitor group 20 is trimmed. The Therefore, a capacitance value that is almost equal to the differential capacitance value between the first parasitic capacitance 31 and the second parasitic capacitance 32 is easily realized.

  The voltage Vclamp1 is usually a power supply voltage for the buffer amplifier 22 and the buffer amplifier 23.

  In FIG. 2, the capacitor group 20 is connected to the initial voltage common output line 11, but may be connected to the optical signal common output line 10. At this time, the capacitance group 20 is connected to the optical signal common output line 10 and the initial voltage common output line 11 in which the parasitic capacitance is smaller.

  In FIG. 4, all the capacitors 20a are connected to the optical signal common output line 10 or the initial voltage common output line 11. However, some of the capacitors 20a may be connected. At this time, the capacitors 20 are connected so that the capacitance value of the capacitance group 20 is substantially equal to the differential capacitance value between the first parasitic capacitance 31 and the second parasitic capacitance 32.

  In FIG. 1, a photodiode is used, but a phototransistor may be used.

It is a circuit diagram which shows a photoelectric conversion unit. It is a circuit diagram which shows the front | former part of a photoelectric conversion apparatus. It is a circuit diagram which shows the back | latter stage part of a photoelectric conversion apparatus. It is a figure which shows a 1st capacity | capacitance group. It is a figure which shows a 2nd capacity | capacitance group.

Explanation of symbols

30 photoelectric conversion unit 10 optical signal common output line 11 initial voltage common output line 18, 19 switch 20 capacitance group 31 first parasitic capacitance 32 second parasitic capacitance

Claims (3)

In a photoelectric conversion device that outputs an output voltage based on incident light,
Optical signal output means for outputting an optical signal based on the incident light;
Reset means connected to the output terminal of the optical signal output means, and resetting the voltage of the output terminal of the optical signal output means to a predetermined initial voltage;
Amplifying means connected to an output terminal of the optical signal output means, amplifying the optical signal to output an amplified optical signal, amplifying the initial voltage and outputting an amplified initial voltage;
An optical signal holding means connected to the output terminal of the amplifying means for holding the amplified optical signal;
A plurality of photoelectric conversion units having an initial voltage holding means connected to the output terminal of the amplifying means and holding the amplified initial voltage;
An optical signal common output line connected in common to all the photoelectric conversion units, outputting each amplified optical signal from each photoelectric conversion unit in time series, and having a first parasitic capacitance;
Commonly connected to all the photoelectric conversion units, outputs each amplified initial voltage from each photoelectric conversion unit in time series, an initial voltage common output line having a second parasitic capacitance,
An adjustment capacitor connected to the optical signal common output line or the initial voltage common output line and having a capacitance value substantially equal to a differential capacitance value between the first parasitic capacitance and the second parasitic capacitance;
A subtracting amplifier for subtracting the amplified initial voltage from the amplified optical signal;
A photoelectric conversion device comprising:   2. The adjustment capacitor has a plurality of capacitors, and each of the plurality of capacitors is connected to the optical signal common output line or the initial voltage common output line through a metal wiring. Photoelectric conversion device.   2. The adjustment capacitor has a plurality of capacitors, and the plurality of capacitors are connected to the optical signal common output line or the initial voltage common output line through a switch circuit, respectively. Photoelectric conversion device.

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